Borisov Andrei B, Raeker Maide O, Kontrogianni-Konstantopoulos Aikaterini, Yang Kun, Kurnit David M, Bloch Robert J, Russell Mark W
Department of Pediatrics and Communicable Diseases, University of Michigan Medical School, Ann Arbor 48109, USA.
Biochem Biophys Res Commun. 2003 Oct 24;310(3):910-8. doi: 10.1016/j.bbrc.2003.09.035.
Obscurin and obscurin myosin light chain kinase (MLCK) are two recently identified muscle proteins encoded by the same gene cluster. The production of obscurin, which contains a Rho-guanine exchange factor (GEF)-like sequence, and obscurin-MLCK by this cluster suggests that these novel genes may be involved in signal transduction cascades that control adaptive and compensatory responses of the heart. The goal of the present study was to investigate the transcriptional response of the obscurin gene cluster to the initiation of myocardial hypertrophy induced in mice by aortic constriction. The transcriptional activity of the obscurin genes was examined using reverse-transcriptase primed quantitative PCR. We found that the transcripts encoding the obscurin Rho-GEF and the obscurin-MLCK internal serine-threonine kinase II (SK II) domains were significantly upregulated following aortic constriction. The expression of Rho-GEF-containing transcripts at different stages of the hypertrophic growth exceeded the control levels by 2- to 6-fold. Following the induction of hypertrophy, the quantity of the SK II-encoding transcripts increased 10-fold by 24h and 16-fold by 48h, then decreased by day 7, and returned to the control level by day 56. The quantity of the carboxy terminal obscurin-MLCK transcripts encoding for SK I increased 2-fold by day 2 and returned to the control values at later stages. Immunolocalization of obscurin, which contains Rho-GEF domain, in cardiomyocytes during pharmacologically induced hypertrophic growth in vitro demonstrated that the expression was topographically associated with the growing myofibrils and with the sites of initiation and progression of myofibrillogenesis at the periphery of the sarcoplasm. This suggests that upregulation of obscurin synthesis is associated with the formation of additional amounts of contractile structures during cardiac hypertrophy. Thus, the obscurin gene cluster represents a new example of an operon that encodes differentially regulated structural and signaling proteins implicated in the control of assembly and adaptive remodeling of myofibrils during normal and hypertrophic growth.
obscurin和obscurin肌球蛋白轻链激酶（MLCK）是最近发现的由同一基因簇编码的两种肌肉蛋白。该基因簇产生含有Rho鸟嘌呤交换因子（GEF）样序列的obscurin和obscurin-MLCK，这表明这些新基因可能参与了控制心脏适应性和代偿性反应的信号转导级联反应。本研究的目的是探讨obscurin基因簇对小鼠主动脉缩窄诱导的心肌肥大起始的转录反应。使用逆转录酶引发的定量PCR检测obscurin基因的转录活性。我们发现，编码obscurin Rho-GEF和obscurin-MLCK内部丝氨酸-苏氨酸激酶II（SK II）结构域的转录本在主动脉缩窄后显著上调。肥厚生长不同阶段含Rho-GEF转录本的表达比对照水平高出2至6倍。肥大诱导后，编码SK II的转录本数量在24小时增加了10倍，在48小时增加了16倍，然后在第7天下降，并在第56天恢复到对照水平。编码SK I的羧基末端obscurin-MLCK转录本数量在第2天增加了2倍，并在后期恢复到对照值。在体外药理学诱导的肥大生长过程中，对心肌细胞中含有Rho-GEF结构域的obscurin进行免疫定位，结果表明该表达在拓扑学上与生长的肌原纤维以及肌浆外周肌原纤维形成的起始和进展部位相关。这表明obscurin合成的上调与心脏肥大期间额外收缩结构的形成有关。因此，obscurin基因簇代表了一个操纵子的新例子，该操纵子编码在正常和肥大生长过程中参与肌原纤维组装和适应性重塑控制的差异调节结构和信号蛋白。
